Electric switch



Sept. 29, 1953 R. H. KINGDON ELECTRIC SWITCH 5 Sheets-Sheet 1 Filed July14, 1950 INVENTOR id/f fl/I'ri BY Sept. 29, 1953 R. H. KINGDON ELECTRICSWITCH 3 Sheets-Sheet 2 Filed July 14, 1950 a ray/vii.

Filed July 1950 3 Sheets-s 3 Z' 3 M Q [I T A? 1/2 I;

A; x 2/ AL: I; #7 24 i i Patented Sept. 29, 1953 Ralph H. Kingdon,Detroit, Mich., assignor to Square D Company, Detroit, Mich., .acorporation of .Michigan Application July1 4, 1950, Serial No. 173,820

21 Claims.

. the switch.

A further object of this invention is to provide an improved formofconstruction for a pivoted blade-member providing .a switching surfaceon its end edge entering along its longitudinal axis to minimize arcsuppressor opening.

Further objectsand features of :the invention will be readily apparenttothose skilled in the art from the specification and appended drawingsillustrating certain preferred embodiments in which:

Figure 1 is a front view of the switch with the cover removed showingtheimproved form of the contact cover and are suppressor.

Figure 2is a verticalsectional view along line II-II of Figure 1 showingthe electrical switch in the closed circuit position.

Figure 3 is a vertical sectional view similar to Figure 2 but showingthe electrical switch in the open circuit position.

Figure 4 is a vertical sectional view of the contact cover along lineIV-IV of Figure 2.

Figure 5 is a vertical sectional view with the contact cover and aresuppressor swung open to provide access to the contacts and terminals.

Figure 6 is a horizontal sectional view along line VI .VI.of Figure 1.

Figure '7 is a vertical sectional view alongline VII-VII of Figure 1showing the switch-operating mechanism.

The invention is specifically illustrated in an outer enclosing metalbox -2 within which is.

mounted an insulating base I withasecond insulating member '3mountedtherein carrying fuse clips and terminals and spaced'from the insulatingbase I in such a manner-as to receive fuses extending from fuse clips I3on the insulating base I.

Mounted on the insulating base I by means of screws 4 area pluralityofstationary contact jaws 5 and conducting stripst. Mountedonthe oppositeends of conducting strips 6 by means of :passes.

screws Tare terminal connectors 8. In line' with and spaced from thestationary contact jaws 5, hinge jaws 9and conducting striplI-aremounted on the-insulating base I by means of screws [2, conductingistrip II :being connected to the fuse clips I3 by means of screws I4.Pivotally mounted within the hinge jaws .9zbyzmeansof hollow rivets I5aresubstantially Yeshapediblad'e members It, the hollow rivets I5:passing :through legs I1 of the blade members 1:6. The other l'egs I8of the blade members IB engagetheistationary contact Jews '5 whentheswitchis inithe closed position. Extensions of :the bases iof -the:blade members It have-recesses I9 .cutthereiniwhich receive aninsulating .bar 2I embracing the :oper'ating bail 22.

'CoVeling the :stationary contact jaws t5 and the terminals 8 is 'aslotted insulating cover 223 which may be secured to the insulating base5| by suitable means such asscrews-iu. .Secured in the insulating cover23 by .anyfsuitablez'means such as azsealing cement-at 538 are a pairofresilient-strips 25 having their free end-bentover so as i to produceLDI'OIlgS 2:6 which engage within the hollow rivets I5'as showninFigures 1-and'5. The insulating cover 23 has:s1ol;s-'21 through whichlegs I8 .of'the blade members l6 pass to engage jaws 5. 'The'uppenbackwall-of the insulating cover 23 hasirecesses fl: cut therein .suchthatthe recesses 28ers complementarywith similar recesses 29inithe=insulating base I in-which the stationary contact jaws'5 andtheiterminals 8 are mounted.

Shoulders 3| are provided in the recesses 28 against which .U -shapedrmagnetic metal plates 32 are-mounted'in suchamanner-as to embrace thelegs I-Bofthe blade-members I'6 when the switch is in the closedposition. Ridges .33, :34, and-35 hold-the plates 32-againstthe-shoulders 3| andcutout portions in the ridges 33 and receivefingers-"$1 atthe-ends of thelegsofiplates 32 to retainthe. plates inposition.

The switch operating mechanism as shown in Figures 1 and 7 consistsof anoperator e39. having a handle 4| and afiat disclikeportion 42 pivoted onthe sidewallof theenclosingboxl by meanseof a threaded shaft 43.andnut-44.

Upon'the inside-wall'of the box-2-ismounted a shielding and supportingbracket59 in spaced relation thereto. Between the bracket 59 and the boxside-wall ismounted a-shaft 48 withthe operating disc 42 provided with.a suitable .cutout portion, not shown,.through which theshaft Upon theshaft-48 -.is pivotallymounted an intermediate operating plate 49 andone end of the operating bail 22, the other end of the bail beingpivoted in the box wall. The plate 49 is provided with a pin 46extending therefrom into engagement with a cutout portion, not shown, inthe disc 42 so as to effect a lost motion connection therewith. Theplate 49 is also provided with a pair of spaced flanges i and 52embracing a leg of the bail 22 so as to provide a lost motion connectiontherewith. A spring guide 53, about which is disposed a main operatingspring 6|, is slidably mounted in a guide 50 swivelled on the side wallof the enclosing box and has a pin 54 on its other end received Within aslot 55 in the intermediate operating plate 49. A light spring 56 hasits opposite ends connected to the plate 49 at 58 and to the disc 42 at51 so as to provide a resilient connection between the plate and disc soas to insure handle position and assist overcenter movement of the mainoperating 2 spring 6|.

A latch 62 is biased by a spring 65 and carries a flange 63 engageablewith a suitable notch, not shown, in the disc 42 to normally preventoperation of the contacts to closed position when the box cover is open,the cover engaging and moving the latch to inoperative position when inthe closed position.

The parts shown in Figures 1, 2, 4, 6 and 'I are in the closed circuitor contacts engaged position, with the legs 18 of the blade members Itengaged with the contact jaws 5. To open the contacts, the handle 41 ismoved downwardly as viewed in Figure 1 and in a clockwise direction asviewed in Figures 2 and '7. This rotates the disc 42 into engagementwith pin 46 to effect rotation of the operating plate 49 also in aclockwise direction as viewed in Figure 7. As plate 49 rotates, it willrotate the spring guide 53 in a counter-clockwise direction and willmove the flange 5! into engagement with the bail 22 so that there willbe formed a direct positive connection between handle l4 and switchblades IE to start the movements of the legs [8 out of the jaws 5.Before the blade leaves the jaws, the main operating spring 61 passesover center assisted by spring 56 and effects a rapid movement of theplate 49, bail 22 and switching blade 16 into the 01f position of Figure3. In closing the contacts, a reverse action of the operating mechanismtakes place to effect snap movement of the switching blades intoengagement with the contact jaws.

As has been previously described, the blade members l6 are pivotallymounted within the jaws 9 on hollow rivets I5 through legs I1 of theblade members 16 with the other legs [8 of the blade members disposed toengage the stationary contact jaws 5 which are mounted on the insulatingbase I in line with the hinge jaws 9. The slotted insulating cover 23 ispivotally mounted to the hollow rivets l5 by means of the prongs 26 onresilient strips so as to fit flush on the surface of the insulatingbase I with the recesses 28 in complementary relationship with recesses29 in the insulating base I. The complementary recesses 28 and 29 thusform are chambers about the contact jaws 5. The contacting legs [6 passthrough narrow slots 21 through the insulating cover 23 which slotsinhibit passage of the arc forwardly of the cover 23 and with the wallsof the slots serving to cool ionized gases which tend to expel throughthe slots 21. Within the chambers formed by the recesses 28 and 29, theU-shaped magnetic plates 32 are magnetized by the insulating base I bymeans of the flow of arcing current between their legs to react with thearcs to draw them downwardly Within the chambers toward the bights ofthe Us and thus inhibit passage of arc gases from the tops of thechambers and thus tend to pre vent fiashover between poles.

A distinctive feature of applicants switch lies in the formation of legsH and H! of member I6 such that the legs l8 enter the slots 21 andengage jaws 5 from an end edge thereof and along the longitudinal axisof the contacting edge as distinguished from a side edge and/ortransverse axis of the contacting leg. This construction obviouslyminimizes the size of the slots through the insulating cover necessaryto provide passage for the switching legs and also permits the properplacing of the U-shaped magnetic plates with their bights positioned toretain the arcs within the arc chambers.

In Figure 5 the insulating cover 23 is shown in its open positionproviding access to the contact jaws 5 and the terminal connectors 83.It will be noted that in this position the insulating cover 23 issupported on the switch by means of the prongs 26 on the resilientstrips 25 engaging in the hollow rivets l5. With the switch in the offposition, the screws 24 are loosened and the insulating cover swung tothe open position of Figure 5, pivoting about the engagement of theprongs 26 in the rivets l5. After whatever manipulation or inspection ofthe jaws 5 and connectors 8 has been accomplished, the cover 23 is swungback counterclockwise into the position of Figure 3 and the studsretightened to place the switch again in operative condition.

While certain preferred embodiments of the invention have beenspecifically disclosed, it is understood that the invention is notlimited thereto, as many variations will be readily apparent to thoseskilled in the art and the invention is to be given its broadestpossible interpretation within the terms of the following claims.

What is claimed is:

1. An electrical switch comprising in combination, an insulating base,stationary contacts and terminals mounted on said base, substantiallyY-shaped blade-members, said blade members pivotally mounted on saidbase adjacent to the end of one leg and having their other legcooperating with a stationary contact, an insulating cover mounted overthe stationary contacts and terminals, said insulating cover havingslots therethrough through which the blade members travel to contact thestationary contacts, and means pivotally mounting said cover at thepivotal mounting of said blade members so that it will swing to uncoverthe contacts and terminals While remaining supported at said pivotalmounting.

2. An electrical switch comprising in combination, an insulating base,stationary contacts and terminals mounted on said base, substantiallyY-shaped blade members, said blade members pivotally mounted on the baseadjacent the end of one leg with the end of its other leg cooperatingwith a stationary contact, operating means insulated from said blademembers and operable upon said blade members to open and close saidelectrical switch, an insulating cover for said stationary contacts andterminals hinged at the pivotal mounting of said blade members andhaving slots therethrough through which said blade members travel, andmagnetic blowout means mounted in said insulating cover for directingc.) an are which may be formed between said sta tionary contacts andsaid blade members away from said terminals and toward said insulatingcover.

3. An electrical switch comprising in combination, an insulating basehaving cutout portions therein, stationary contacts and terminalsmounted in said cutout portions, substantially Y-shaped blade members,said blade members pivotally mounted on the base adjacent the end of oneleg and engaging said stationary contacts adjacent the end of the otherleg, a bail member insulated from and operative upon said blade membersto join said blade members for unitary operation, and an insulatingcover for said insulating base hinged to the point of pivotal mountingof said blade members and having slots therethrough through which saidcontact legs of said blade members travel.

4. An electrical switch comprising in combination, an insulating bashaving a plurality of cutout portions therein, stationary contacts andterminals mounted in each of said cutout port s, substantially Y-shapedblade members, said class members pivotally mounted on the base adjacentthe end or one leg and engageable with said stationary contacts adjacentthe end or the leg, an operating bail member insulated. ire-m ardoperative upon said blade members to join blade members for unitaryoperation, an in lating cover plate hinged to the pivotal mo ing of thesaid blade members, said insul cover plate having slots therethrough thrwhich the blade members travel to engage sad stationary contacts, andU-shaped m ti le arc suppressor members mounted on s. ing cover platearound said slots with is directed toward the pivotal mounting ofmembers.

5. An electrical switch comprising in tion, an insulating base,stationary contacts terminals mounted on said base, substant' .11 7 r'--shaped blade members each pivotally mounted on the base adjacent the endof one leg and having its other leg cooperating with a stationarycontact, insulating cover, resilient in hers in said insulating cover,said in ulating cover hinged to the pivotal mountings of said blademembers by means of said resilient spring members, said cover coveringsaid stationary contacts and terminals, and having slots therethroughthrough which the blade members travel to engage said stationarycontacts.

6. An electrical switch comprising in combination, an insulating base,stationary contacts and terminals mounted on said base, blade memberscooperating with said stationary contact-s, stationary posts mounted onsaid base in line with said contacts and terminals, said blade memberspivotally mounted to said stationary p. s by means of hollow rivets, aninsulating cover .1: nber for said stationary contacts having mountedthereon resilient strips carrying pro s, silient strips pivotallymounting said in cover to said stationary posts by engagement saidprongs in said hollow rivets, and operating means for engaging anddisengaging blade members and said stationary contacts.

'7. An electric switch comp-rising in combination, an insulating base,stationary contacts and terminals mounted on said base, blade members,stationary hinge posts mounted on said base in line with said contacts,said blade members pivotally mounted to said stationary posts andcooperating with said stationary contacts, an insulating cover for saidstationary contacts pivotally mounted to said stationary posts at thepivotal mounting of said blade members so as to swing to uncover thecontacts and terminals while supported on said stationary post, andoperating means for engaging and disengaging said blade members and saidstationary contacts.

8. An electrical switch comprising in combination, an insulating basehaving a plurality of cutcnt portions therein providing unrestrictedopenings to the top of said insulating base, stationary contacts andterminals mounted in each of said cutout portions, substantiallyY-shaped blade members cooperating with said contacts, said blademembers having a recess in the bas thereof, said blade members pivotallymounted to the base adjacent to the end of one leg and having theirother leg entering the stationary contact at the end edge asdistinguished from the side edge thereof and interposing the endportions of the leg its-e11 in engagement with the stationary contacts,an insulating crossbar joining said blade members for unitary operationby engagement in said recess in said blade members, an operating bailengaging said insulating bar providing a means for opening and closingsaid electrical switch, insulating cover for said insulating base havingcutout portions therein providing unrestricted openings to the top ofsaid insulating cover complementary with the cutout portions andopenings in the insulating base, slots through said cover in line withsaid stationary contacts through which said blade members travel, andmagnetizable, U-shaped, metallic plates mounted in the cutout portionsof the cover with their legs embracing the path of movement of the blademembers and pointing into said unrestricted openings in said insulatingcover and their bights directed toward the pivotal mounting of the blademembers.

9. An electrical switch comprising in combination, an insulating basehaving a plurality of cutcutout portions, substantially Y-shaped blademembers cooperating with said contacts, said blade members having arecess in the base thereof, said blade members pivotally mounted to thebase adjacent to the end of one leg and having their other leg enteringthe stationary contact at the end edge as distinguished from the sideedge thereof and inter-posing the end portions of the leg itself inengagement with the stationary contacts, an insulating crossbar joiningsaid blade members for unitary operation by engagement in said recess insaid blade members, an operating bail engaging said insulating bar andproviding means for opening and closing said electrical switch, aninsulating cover for said insulating base having cutout portions thereinand an unrestricted opening to the top of said insulating covercomplementary with said cutout portions and openings in said insulatingbase, a plurality of slots through said cover in line with saidstationary contacts through which said blade members travel, meanspivotally mounting said cover on said base, and magnetizable, U-shaped,metallic plates mounted in the cutout portions of the cover with theirlegs embracing the path of movement of said blade members and pointing Lcutout portions therein, stationary contacts and terminals mounted ineach of said cutout portions, substantially Y-shaped blade memberscooperating with said contacts, said blade members having a recess inthe base thereof, said blade members pivotally mounted on the baseadjacent to the end of one leg and having its other leg engaging thestationary contact along the longitudinal aXis of said other leg, aninsulating bar joining said blade members for unitary operation byengagement in said recess in said blade members, an operating bailengaging said insulating bar and providing means for opening and closingsaid electrical switch, an insulating cover for said insulating basehaving cutout portions therein complementary with the cutout portions insaid base, slots through said cover in line with said stationarycontacts through which said switch blade members travel, means pivotallymounting said cover on the pivotal mounting of said blade members sothat said cover will swing to uncover the contacts and terminals whilesupported on the base, and a plurality of magnetizable, U- shaped,metallic plates mounted in the cutout portions of the cover with theirlegs embracing the path of movement of said blade members and theirbights directed toward the pivotal mounting of said blade members.

11. An electrical switch comprising in combination, an insulating basehaving a plurality of cutout portions therein providing unrestrictedopening to the top of said insulating base, stationary contacts andterminals mounted in each of said cutout portions, a plurality ofsubstantially Y-shaped blade members cooperating with said contacts,said blade members having a recess in the base thereof, said blademembers pivotally mounted to the base adjacent the end of one leg andhaving its other leg entering the stationary contact at the end edge asdistinguished from the side edge thereof and interposing the endportions of the leg itself in engagement with the stationary contacts,an insulating crossbar joining said blade members for unitary operationby engagement in said recess in said blade members, an

operating bail engaging said insulating bar providing a means foropening and closing said electrical switch, an insulating cover for saidinsulating base having cutout portions therein and an unrestrictedopening to the top complementary with said cutout portions and openingsin said insulating base, a plurality of slots through said cover in linewith said stationar contacts through which said blade members travel,and

means pivotally mounting said cover on the pivotal mounting of saidblade members so that said cover may swing to uncover the contacts andterminals while supported on said pivotal mounting, magnetizable,U-shaped, metallic plates mounted in the cutout portions of saidinsulating cover with their legs embracing the path of movement of theswitch blades and pointing into said unrestricted opening and with theirbights directed toward the pivotal mounting of the switch blade.

12. An electrical switch comprising in combination, an insulating base,stationary contacts and terminals mounted on said base, substantiallyY-shaped blade members cooperating with said stationary contacts,stationary hinge jaws mounted on said base, said blade members pivotallymounted to said hinge jaws by means of hollow rivets, an insulatingcover member for said stationary contacts, resilient strips carryingprongs mounted to said cover member, said insulating cover pivotallymounted to said hinge jaws by means of said resilient strips engagingsaid hollow' rivets whereby the insulating cover may be swung to uncoverthe contacts and terminals, and means for operating said blade membersinto and out of engagement with said stationary contacts.

13. An electrical switch comprising in combination, an insulating basehaving a plurality of cutout portions therein, stationary contacts andterminals mounted in each of said cutout portions, stationary hinge jawsin line with said stationary contacts, a plurality of substantiallyY-shaped blade members, said blade members pivotally mounted on saidstationary hinge jaws by means of a hollow rivet through said hinge jawand one leg of said blade member, the other leg of said blade memberengaging the stationary contact along its longitudinal axis, aninsulating cover for said insulating base, resilient strips carryingprongs mounted on said insulating cover, said prongs engaging saidhollow rivets so that said insulating cover may be swung to uncover thecontacts and terminals and may be bodily removed by disengagement ofsaid prongs and said hollow rivets, slots through said insulating coverin line with said stationary contacts through which said blade memberstravel, a plurality of 'U -shaped, metallic plates mounted in saidinsulating cover with their legs embracing the path of movement of saidblade members and their bights directed toward the pivotal mounting ofsaid blade members.

14. An electrical switch comprising in combination, an insulating base,stationary contacts and terminals mounted on said base, stationary hingejaws mounted on said base in line with said stationary contacts andterminals, substantially Y-shaped blade members cooperating with astationary contact and pivotally mounted to said stationary hinge jawsby means of hollow rivets, an insulating cover member for saidstationary contacts, resilient strips carrying prongs mounted on saidinsulating cover, said insulating cover pivotally mounted to said hingejaws by means of said resilient strips carrying prongs engaging saidhollow rivets so that said insulating cover may be swung to uncover thecontacts and terminals and may be bodily removed by disengagement of theprongs and the hollow rivets.

15. An electrical switch comprising in combination, an insulating base,a plurality of stationary contact jaws and terminals mounted on saidbase, a plurality of substantially Y-shaped blade members cooperatingwith said stationary contact jaws, said blade members having recesses inthe base legs thereof, each of said blade members being pivotallymounted on the base adjacent to the end of one open leg and having itsother open leg entering the contact jaw along its longitudinal axis andat its end edge as distinguished from the side edge thereof, andinterposing the end portions of the leg itself in engagement with thestationary contact jaw.

16. An electrical switch comprising in combination, an insulating base,a plurality of station: ary contact jaws and terminals mounted on saidinsulating base, a plurality of substantially Y-shaped blade memberscooperating with said contact jaws, said blade members having recessesin the base legs thereof, each of said switch blade members beingpivotally mounted on the base adjacent to the end of an open leg andhaving its r p leg ing the stationary contact jaw along the longitudinalaxis of said leg and at its end edge as distinguished from the side edgethereof and interposing the end portions of the leg itself in engagementwith the stationary contact jaw, an insulating bar joining said blademembers for unitary operation by engagement in said recesses in saidblade members, and an operating bail engaging said insulating bar andproviding means for opening and closing said electric switch.

17. An electrical switch comprising in combination, an insulating base,a plurality of sta tionary contact jaws and terminals mounted on saidinsulating base, a plurality of substantially Y-shaped blade memberscooperating with said contact jaws, said blade members having recessesin the base legs thereof, each of said switch blade members beingpivotally mounted on the base adjacent to the end of an open leg andhaving its other open leg engaging the stationary con tact jaw along thelongitudinal axis of said leg and at its end edge as distinguished fromthe side edge thereof and interposing the end portions of the leg itselfin engagement with the stationary contact jaw, an insulating bar joiningsaid blade members for unitary operation by engagement in said recessesin said blade members, an operating bail engaging said insulating barand providing means for opening and closing said electric switch, and aninsulating cover in front of said stationary contact jaws and havingslots therethrough in line with the stationary contact jaws throughwhich said other open legs of the blade members travel in engaging anddisengaging the contact jaws.

18. An electrical switch comprising in combination, an insulating basehaving a plurality of cutout portions therein, a plurality of stationarycontact jaws and terminals mounted in each of said cutout portions, aplurality of substantially Y-shaped blade members cooperating with saidcontact jaws, said blade members having recesses in the base legsthereof, each of said switch blade members being pivotally mounted onthe base adjacent to the end of an open leg and having its other openleg engaging a stationary contact jaw along the longitudinal axis ofsaid leg and at its end edge as distinguished from the side edge thereofand interposing the end portion of the leg itself in engagement with thestationary contact jaw, means joining said blade members for unitaryoperation into and out of engagement with the contact jaw to perform theswitching operation, and an insulating cover for said insulating basehaving cutout portions therein complementary with the cutout portions insaid base, said cover having slots therethrough in line with saidstationary contacts through which said other open legs of said blademembers travel as they engage and disengage the stationary contact Jaws.

19. In an electrical switch, an insulating base, a plurality ofstationary contact jaws and terminals mounted upon said base, aplurality of conducting blade members cooperating with said stationarycontact jaws, said blade members being pivotally mounted on the base forrotative movement into and out of engagement with the stationary contactjaws, the contact engaging portions of the blade members beingconstituted by legs disposed to enter the contact jaws along thelongitudinal axis of the legs and at their end edges as distinguishedfrom the side edges thereof, means for rotating said blade members asdistinguished into and out of engagement with the contact jaws to eifectthe switching operation, and an insulating cover in front of saidstationary contact jaws and cooperating with the insulating base to formindividual chambers about the jaws, said cover having slotstherethrough, major with respect to the front wall and minor withrespect to the bottom wall, through which the legs of the blade memberspass in engaging and disengaging the contacts.

20. In an electrical switch, an insulating base, a plurality ofstationary contact jaws and terminals mounted on said base, a pluralityof conducting blade members pivotally mounted on said base for rotativemovement into and out of engagement with the stationary contact jaws,each of said blade members having one portion remote from saidstationary contact jaws provided with a pivotal mounting at its end anda contact portion remote from said pivot end disposed at a substantialangle to said one portion and entering the stationary contact jaws alongthe longitudinal aXis of the contact portion and at its end edge fromthe side edge thereof, an insulating cover cooperating with theinsulating base to form individual contact chambers about said contactjaws, said insulating cover having slots therein, major with respect tothe front wall thereof and minor with respect to the bottom wall, thecontact portions of said blade members passing through said slots withthe longitudinal axes of the contact portions substantially at rightangles to the front wall of the insulating cover, and means joining saidblade members for common movement as a unit into and out of engagementwith the stationary contact jaws to perform the switching operation.

21. In an electric switch, an insulating base, a plurality of stationarycontact jaws and terminals mounted on said base, a plurality ofconducting blade members pivotally mounted on the base for rotativemovement into and out of engagement with the stationary contact jaws,each of said blade members having one portion remote from saidstationary contact jaws provided with a pivotal mounting at its end anda contact portion remote from said pivot and disposed at a substantialangle to said one portion and entering the stationary contact jaws alongthe longitudinal axis of the contact portion and at its end edge asdistinguished from the side edge thereof, extending portions on saidblade members substantially in line with the contact portions thereof,recesses in said extending portions, insulating means engaged in saidrecesses to join said blades for common movement, and an operating bailengaging said insulating means to effect operation of the blades toperform the switching operation.

RALPH H. KINGDON.

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